1. Field of Invention
The present invention relates to a lighting device and, more particularly, to a high-power light emitting diode (LED) lighting device with enhanced thermal management and a method of fabricating the same.
2. Description of Related Art
One of the key advantages of LED-based lighting is that it exhibits a higher efficiency in terms of light output per unit power input as compared to traditional incandescent lighting. Moreover, recent advances in LED-based lighting technology now make it possible for LED-based lighting to exhibit higher efficiency in such terms than standard fluorescent lighting. LED-based lighting is also less prone to damage due to vibration and has a longer service life.
Generally speaking, high-power LED's are required for general lighting applications. In the present specification and in the accompanying claims, the phrase “high-power LED” means an LED that is capable of continuous use at greater than or equal to one watt (≧1 W) of electrical power. It is often necessary to use two or more high-power LED's in an array to provide the desired light output.
The use of high-power LED's presents a problem. Unlike incandescent lighting sources, which radiate much of their energy as heat and are thus capable of operating at high temperatures, high-power LED's need to operate within a relatively narrow temperature range. And, because high-power LED's do not have perfect light-emission efficiency in converting electrical energy to light energy, some of the supplied electrical power is converted into heat. This heat, if not properly dissipated, can increase the operating temperature of the high-power LED, which can significantly alter and/or permanently degrade the operating characteristics of the high-power LED. There are four critical characteristics of a high-power LED that are affected by its operating temperature:                First, it is known that the operating temperature of an LED is inversely proportional to the energy bandgap, and that the energy bandgap is inversely proportional to the wavelength of light emitted from the LED. Accordingly, as the operating temperature of the high-power LED increases, the energy bandgap becomes narrower, and thus the wavelength of the emitted light increases. Therefore, when a high-power LED experiences an increase in its operating temperature, the wavelength of the light may increase by several nanometers. This phenomenon is called “a color shift”. Consequently, when the heat generated by the high-power LED is not efficiently dissipated away from the device, light of the desired color cannot be obtained due to the color shift by the high-power LED.        Second, the brightness efficiency of light emitted from a high-power LED decreases as the operating temperature of the high-power LED increases.        Third, a high operating temperature accelerates a permanent reduction in light output from the LED referred to as lumen degradation. This reduction in light output is caused by degradation of the packaging materials and lattice changes in the epilayer of the die (which is also sometimes referred to in the art as an “LED chip”).        Fourth, high operating temperatures decrease the overall reliability of the device due primarily to thermal stress from thermal coefficient of expansion (“TCE”) mismatches between the LED die and packaging materials.        
While the effects of improperly managed operating temperatures on the first two critical characteristics of a high-power LED are generally considered to be temporary, the last two critical characteristics affected by improperly managed operating temperatures are permanent. Thus, it is essential to dissipate heat from high-power LED lighting devices.